Automatic intermittent gas-lift of liquids



Dec. 25, 1962 .1. K. wELcHoN 3,070,033

` AUTOMATIC INTERMITTENT GAS-LIFT OF LIQUIDS Filed June 16, 1960 2 Sheets-Sheet 1 TIMER l l I l CYCLELER 36 35 33 CONTROL 32( L INVENTOR. F/G. .MMWELCHON BY H-Lwlsm E` M A TTORNEKS' Dec. 25, 1962 Filed June 16, 1960 J. K. WELCHON AUTOMATIC INTERMITTENT GAS-LIFT OF L'IQUIDS 2 Sheets-Sheet 2 INVEN] OR. JK. WELCHON A 7' TORNE'YS ntic 3,070,d33 Patented oec. ze, rss2 3,070,033 AUTOMAHC lNTERMITTENT GAS-LIFE` F LIQUIDS .laines l. Welchen, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Filed lune i6, 1960, Ser. No. 36,599 6 Claims. (Cl. 10S- 232) This invention relates to the lifting of liquids from wells, such as oil Wells and the like. In another aspect, it relates to a method and apparatus for the automatic intermittent gas-lift of liquids from wells, such as an oil well penetrating a low pressure producing formation. ln a further aspect it relates to a method and apparatus for automatically adjusting and controlling the intermittent supply of compressed gas to a gas-lift well ,penetrating a low pressure oil producing formation, so as to control and increase the flow of oil therefrom.

When gas pressure is no longer suiiicient in the oil producing zone to maintain the natural flow of oil from a producing well at a rate sufficient to produce a desired quantity of oil, it is necessary to resort to other means for producing the oil, such as gas-lift. One type of gaslift is the intermittent gas-lift method, which is the concern of this application.

ln the production of oil from wells by the intermittent gas-lift method, compressed gas is usually injected intermittently at the well head into the annulus between the production tubing and outer casing and thence through gas-lift valves into tne production tubing at a point below the level of the column of oil which has accumulated in the tubing. The gas introduced into the tubing forces a column of the accumulated oil in the form of a slug to the surface of the well from whence the produced oil, and injected gas, are conveyed to suitable gas-liquid separation means for the recovery of the oil. After producing the slug of oil, oil from the formation is allowed to accumulate once more in the production tubing to a level above the point where the lift gas is injected thereinto, and the gas-lift cycle is repeated.

Many methods have been proposed, patented, or used for controlling `the frequency of the gas-lift cycle. While many of these methods are satisfactory, they are not without their shortcomings. The oil from the producing formation often does not flow therefrom into the well bore at a fixed rate, and consequently the quantity of oil which can be produced daily varies over the life of the Well. Other factors extant in the bottom of the well also cause variation in the quantity of oil produced. The prior art methods, in an attempt to alter or change the gas-lift cycle frequency in accordance with conditions in the bottom of the well, often require a good deal of surveillance of the operation of the gas-lift well, necessitating an inordinate number of man-hours to keep check on the operation of the gas-lift well in an attempt to maintain desirable production. Some methods of the prior art rely on the manual or semi-automatic control of the gas-lift cycle frequency, cycle corrections being made on the basis of past experience or assumed reservoir conditions. ln general, the frequency of the gas-lift cycle is usually fixed for a substantial length of time, for example between trips to the well head by a lease operator. However, during such intervals, conditions in the well may change adversely, with the result that the well is not producing an optimum amount of oil throughout the fixed interval, and/or the operation of the well is requiring a higher lift gas/oil ratio than is necessary for adequate production.

Accordingly, an object of this invention is to improve the lifting of liquids from wells, such as oil wells and the like. Another object is to provide an improved method and apparatus for the automatic intermittent gas-lift of liquids from wells, such as an oil well penetrating a low pressure producing formation. Another object is to provide an improved method and apparatus for automatically controlling the intermittent supply of compressed gas to a gas-lift well penetrating a low pressure oil producing formation, so as to control and increase the production of oil therefrom. Another object is to automatically adjust the frequency of the gas-lift cycle of a gas-lift well, in accordance with conditions in the bottom of the well, so as to automatically maintain a relatively constant volume of produced oil per gas-lift cycle and constant lift gas/oil ratio. Another object is to produce an optimum amount of oil from a gas-lift Well at an optimum injection gas/produced oil ratio. Other objects and advantages of this invention will become apparent to those skilled in the art from the following discussion, appended claims, and accompanying drawing in which:

FIGURE l is an elevational view, partially in section, illustrating a gas-lift Well with the automatic control means of this invention associated therewith;

FIGURE 2 is a schematic view of one embodiment of the automatic 4control means of this invention which can be used to control the operation of the gas-lift well of FGURE l; and

FGURES 2a, 2b, and 2c illustrate in detail certain portions of FlGURE 2.

The invention will be illustrated herein as applied to the operation of a gas-lift well in the production of oil from a low pressure producing formation, Le., a formation with insullicient pressure to maintain natural ilow of oil at a rate sufficient to produce a desired quantity of oil. However, it should be understood that this invention is not to be unduly limited thereto since it is applicable wherever it is desired to lift liquids from any supply thereof, particularly where it is not desirable or practical to mount the lifting apparatus below the liquid level such as would be encountered in a deep well.

Referring now to FlGURE l, a deep gas-lift well is illustrated. Said gas-lift well comprises a bore hole il penetrating various strata l2, 13 and l5 of a non-produc ing nature, and a low pressure producing formation la. Depending within bore hole ll is an outer casing i6 secured within the bore hole by means of a sheath of cement i7, or the like, to provide a fluid tight seal. The lower ends of the casing 16 and cement sheath 17 can terminate at a point above the producing formation i4 but preferably terminate, as shown, at a point adjacent or below the producing formation. Casing lo and cement sheath i7 can be provided with the usual perforations i8 adjacent the producing formationll so as to allow the flow of oil from the latter into the well; of course, where the lower ends of the casing and cement sheath terminate above the producing formation, so as to provide an open hole, such perforations will be unnecessary. Depending within casing lo is a string of production tubing 19, the lower end thereof terminating in the vicinity of the producing formation ld. Said lower end of tubing i9 can be provided with the usual check valve generally designated 2l `to permit the flow of oil from the formation iti into the lower end of the tubing, but prevent the flow of oil in the reverse direction. The annular space 22 between casing 16 and tubing i9 is sealed by means of packer 23 or the like, the portion of the annular space thereabove serving as a compressed gas reservoir and the portion of the annular space below the packing serving as an oil accumulation zone. One or more gas-lift valves 24, or the like, are affixed to the production tubing 19 at a point above the location of packer 23. A column 26 of accumulated oil is shown 3 'occupying the lower portion of the production tubing 19, said coiumn having an upper level 27.

The upper end of casing i6 is provided with a lift gas supply conduit 28, having an adjustable gas injection valve 29 therein controlling the tlow therethrough, said lift gas supply conduit being connected to a suitable source of lift gas iaving a constant pressure, such as natural gas. The upper end of production tubing 19 passes through casing head 31 and communicates with the usual surface production conduit 32 having the usual flow c0ntrol valve 33 therein. ril`he Well head can also be provided with the usual appurtenances such as pressure gauges, ilow meters, and the like, which have not been illustrated in the interest of brevity. n

The foregoing discussion describes a typical gas-lift well, which by itself forms no part of my invention.

As mentioned hereinbefore, the duration it takes to accumulate a constant volume of oil within the production tubing of a gas-lift well will often vary between gaslift cycles, due to the variable rate of ilow of the oil from the producing formation into the well, and/or due to factors which affect the gas-lift equipment within the well itself, such as the accumulation of paraflin within the production tubing, check valve, formation perforations, etc. Thus, in order to produce an optimum amount of oil during each gas-lift cycle, notwithstanding changes in bottom hole conditions or eciency of the gas-lift equipment within the well, it is necessary to change the frequency of the gas-lift cycle. As mentioned above, the prior art methods of changing the gas-lift frequency rely on past experience or assumed conditions in the well rather than actual conditions in the well, and make manual or semi-automatic adjustments in the gas-lift cycle frequency, often only at infrequent intervals. As a result, such prior art methods do not maintain an optimum and constant volume of oil produced in each gas-lift cycle, the lift gas/oil ratio of such methods being variable.

My invention overcomes the shortcomings of the prior art and automatically adjusts the frequency of the gaslift cycle from cycle-to-cycle in accordance with the exact conditions in the bottom of the well so as to produce a relatively constant volume of produced oil and an optimum lift gas/oil ratio. According to my invention, as shown in FGURE l, the fluid pressure at the upper end of the production tubing is continuously sensed by means of a suitable pressure tap 35 and the pressure is transmitted by pressure line 36 to an automatically adjustable gas-lift cycle controller 37 which is operatively connected to timer 38 which accordingly is capable of being reset from cycle-to-cycle, if necessary, due to conditions in the bottom of the well, so as to control the frequency or opening of injection valve 29.

When a slug of accumulated oil reaches the upper end of the production tubing i9 there will be an abrupt increase in the production tubing pressure, due to the fact that the oil must pass through a restriction, such as that created by valve 33 when the latter is in a partially open position. According to this invention, a signal indicative of this abrupt rise in production tubing pressure is transmitted by pressure tap 35 and pressure line 36 to the automatically adjustable cycle controller 37 and compares it on a time scale with a signal from the opening of the gas injection valve 29. if, during one cycle, in relation to an initial preselected time interval, the rise in tubing pressure occurs too soon after the opening of the gas injection valve 29, indicative of a slug of oil having less than the optimum volume, the timer 38 is automatically adjusted by a iixed increment, so that during the next gaslift cycle the gas injection valve is opened only after the oil within the production tubing i9 has an opportunity to accumulate over a relatively longer period. Conversely, if the production tubing pressure rise occurs later than the preselected time interval, indicative of a slug of oil having volume relatively larger than optimum, the timer 3S is accordingly adjusted by a fixed increment, so that the oil during the next cycle has an opportunity to accumulate over a relatively shorter period. Thus, the timer 38 can be adjusted by an increment each cycle, but only so long as necessary, to make the production tubing pressure rise occur at a proper time in relation to the opening of the gas injection valve. This automatic control maintains a relatively constant optimum volume of produced oil per gas-lift cycle and an optimum injection-gas/pro duced oil ratio,

Any other means which will sense the arrival of the oil at the desired elevation can be used as a pivotal vane or paddle in the production tubing which would be deflected Iby the slug of oil and actuate a switch.

The sequence of events or operations during the controlled gas-lift cycle of this invention may be brieiiy described as follows:

l) The beginning of the cycle starts with the injection of compressed gas into the annulus between the casing and the production tubing, and its subsequent flow through 'the gas-lift valves, the timing of this injection step being based on the conditions in the well as determined during the immediately preceding cycle; a signal indicative of the commencement of the injection step is transmitted to the cycle controller;

(2) Elevation or lifting of the fluid slug Within production tubing, occasioned by the injection of lift therein via the gas-lift valves;

(3) Arrival of the fluid slug at the desired elevation, such as the upper end of the production tubing, causing an abrupt rise in tubing pressure;

(4) Transmittal of a signal indicative of the rise in tubing pressure to the automatically adjustable cycle controller, and the resetting (if necessary) ofthe gas injection valve timer;

(5) Production of the uid slug at the surface;

(6) Bleed-down of the lift gas following the produced fluid slug; and

(7) Accumulation of oil in the production tubing.

the

gas

The above cycle is repeated, starting with injection of lift gas after the oil accumulation interval, the commencement of the next cycle being based on the arrival of the fluid slug at the surface as determined by the preceding cycle.

Reference will now be made to FIGURE 2 for a description of one embodiment of the automatic gas-lift cycle control feature of this invention.

In FIGURE 2, supply gas, such as natural gas or air, having a pressure for example of 20-25 psig., for the purpose of actuating the gas injection valve 29 and cycle controller 37 of FIGURE l, is transmitted via line d,

having a flow control valve 42 therein. The latter is op eratively connected to and controlled by a suitable rnechanical linkage, or the like, such as a cam operated roller device, generaly designated 43, which in turn is op eratively connected to the rotating shaft 44 of lift gas injection timing wheel 46. Rotation of timing wheel i5 is accomplished by means of constant speed motor d?, suitable gear train 48, driving wheel 49 and the ball Si. of a suitable screw driven ball cage mechanism generally designated 52, the later having a screw 53 which can be turned either clockwise or counterclockwise. The screw driven ball cage is shown in detail in FlGURE 2a. By this arrangement, the speed of rotation of timing wheel 46 is determined by the relative location of ball 5l on screw 53; the closer the ball 5i is to the periphery of timing wheel 46, the slower the speed thereof, and, conversely, the closer ball 5l is to the center of timing wheel lio, the faster the speed of the latter. The speed of rotation of the cam mechanism i3 is in direct proportion to the speed of rotation of timing wheel 46, so that the faster the latter is rotated the greater the frequency of the open ing of valve 42 and vice versa.

T he constant speed motor 157 also rotates shaft 5d, having a bevel gear 56 attached thereto. Shaft 5d is operaspinosa tively adapted to complete one full rotation before shaft 44 completes its one full rotation, or in the event that one full rotation of shaft 44 creates a plurality of cycles, then shaft 54 must make one complete rotation each cycle before shaft 44 initiates the next cycle. ln axial alignment with s raft 54 is another shaft 57 having attached to one end thereof a bevel gear 58, which is in close spaced relationship with bevel gear 56. Mounted on shaft 57 are cams 59, 61 and 62, which are rotatable with the shaft 57. Cams 59?, 6l and 62 have associated therewith in close space relationship nozzles of gas lines 63, 64 and 66 respectively, controlling the restriction thereof. Gas line 63 also communicates via branch 67 with Kthe lower end of a piston chamber 63, the latter having reciprocally mounted therein a piston 69. Piston 69 has a rod 7l attached thereto which depends and protrudes from piston chamber 68. The lower end of piston rod 71 has attached thereto a pinion gear 73. An expansion spring 74 tends to force pinion gear 73 into engagement with bevel gears 56, 5S. The upper end of gas line 63 is connected to a supply gas bypass line 76, which in turn is connected to supply gas line 40 upstream of valve 42. The upper end of piston chamber 68 communicates with a gas line 77, which in turn communicates with supply gas line 4l downstream of valve 42, gas line 77 having a suitable bleed line 78 therein.

The pressure sensing line 36, connected to the pressure tap 35 of the production tubing 19 of FIGURE 1, is operatively connected to the lower end of piston chamber 79, the latter having a piston Si rcciprocally disposed therein and suspended on the lower end of piston arm 82. Compression spring 83 tends to force piston 81 downward. The upper end of piston arm S2 is operatively provided with a pivotal appendage or pin 84, the latter being operatively allowed to swing upward out not permitted to swing completely-downward by reason of stop 85. Appendage 34 is operatively adapted to deflect pivotal member 86 when piston arm 82 moves upward, as shown by the directional arrow. This deflection of pivotal member 86 is a momentary occurrence since as soon as appendage 84 moves upward beyond pivotal member 86 the latter is allowed to return to its original position, as shown in the drawing. The other extremity of pivotal member 86 is in close spaced relationship to the open end or nozzle of gas line S7, the latter being operatively connected to gas line 76.

Gas line 76 is also in operative communication via line SS with the upper ends of piston chambers 89, 9i, the latter having reciprocally mounted therein pistons 92, 93, respectively. Depending from pistons 92, 93 and protruding from the lower ends of piston chambers 39, 91 are piston rods 94, 96, respectively, the downward movement of the latter being urged by compression springs 97, 9S, respectively. The lower end of piston chamber 89 is operatively connected to gas line 66, the latter in turn being operatively connected to supply gas bypass line 76 via branch line 99. The lower end of piston chamber 9i operatively communicates with gas line 64, the latter in turn being in communication with bypass line 76 via branch line lill. The lower ends of piston rods 94, 96 are operatively adapted to serve as ratchets or pawls and are in operative contact with ratchet wheels to2, 163, respectively, which in turn are mounted on screw 53. @ne ratchet is mounted on one side of one ratchet wheel and the other ratchet is mounted on the other side of the other ratchet wheel so that upward movement of the iirst ratchet will cause one ratchet wheel to move the screw clockwise, and upward movement of the other ratchet will cause the other ratchet wheel to move the screw counterclockwise. Ball 5i will move either toward the periphery or timing wheel 46 or toward the center thereof, depending upon the direction of rotation of screw 53, le., clockwise or countercloclrwise. Gne-half of this ratchet arrangement is illustrated in detail in FIGURE 2b.

The operation of the automatically adjustable cycle 6 controller and timer of FlGURE 2 will now be described in conjunction with the operation of the gas-lift well of FiGURE 1.

Prior to the beginning of the gas-lift cycle, and during the accumulation of oil within production tubing 19, supply gas from line 4l) is transmitted to lower end of piston chamber 63 via lines 76, 63 and 67; this supply gas is also transmitted to the upper ends of piston chambers 89, 91 via lines 76, 8S, and to the lower ends of piston chambers 89, 9i via lines 76, lill, 64 and lines 76, 99, 66, respectively. At this time, assume that the: nozzles at the ends of lines 63, 64 and 66 are restricted by the projecting portions of cams S9, 6l and 62, respectively; these positions of cams 59, 6l, 62 are shown schematically in FG- URE 2c. The gas pressure admitted to the lower end ot' piston chamber 68 maintains pinion gear 73 out of engagement with bevel gears 56, 58; thus, shaft 57 is not rotating at -this time. When the nozzles of lines 63, 64 and 66 are thus restricted, the gas pressure on opposite sides of pistons 92, 93 will be equalized and ratchets 94, 96 will be held in their lower positions, such as illustrated in FIGURE 2b. During this interval, timing wheel 46 is rotating and the cam mechanism 43 is moving toward its activating position, valve 42 being maintained in its closed position until cam mechanism 43 reaches its activating position.

With valve 42 in its closed position, no gas pressure is transmitted from line 4l via line 77 to the upper end of piston chamber 68. During this interval, only lowpressure is transmitted from the production tubing i9 via line 36, this low pressure being insullcient to move piston 81 upward.

After a sumcient volume of oil has accumulated in production tubing 19, the gas-lift cycle begins. This cycle is initiated when timing wheel 46 has rotated to the extent necessary for cam mechanism 43 to reach its activating position, when it causes the opening of valve 42. Opening of valve 42 permits supply gas from line 4l? to be transmitted via line 41 to injection valve 29, causing the opening thereof with the consequent injection of lift gas into the annular space 22 of the gas-lift well. Valves 42 and 29 are held open while cam mechanism 43 is in its activating position, e.g., l() minutes, as determined by the extent of the projection 45 on the cam mechanism.

The opening of supply gas valve 42 results in the application of gas pressure to the upper end of piston chamber 63 via line 77, this pressure augmenting the downward bias of spring 74 and causing piston 69 to move downward with the consequent engagement of gears 73, 56 and S3 and the rotation of shaft 57. Rotation of cam 59 unrestricts the adjacent nozzle of gas line 63. Further rotation of shaft S7 causes the unrestriction of the nozzles of line 64, 66, respectively. The unrestriction of the nozzles of lines 63, 64 and 66 does not cause any movement of pis-tons 69, 93 and 92, respectively, since the gas pressure thereabove holds the same in their down positions.

After the cam mechanism 43 has moved beyond its activating position, valve 42 is closed, with the consequent termination of lift gas injection into the well. Before or after termination of injection of lift gas, the slug of accumulated oil reaches the surface of production tubing 19 and causes an abrupt increase in tubing pressure. This increase in tubing pressure is transmitted via line 36 to piston chamber 79 causing the upward movement of piston 3l, piston arm 82, and appendage 84. Upward movement of appendage 84 causes pivotal member 86 to pivot and momentarily open the nozzle of line 87 adjacent thereto. This momentary opening of the nozzle at the end of line S7 releases the pressure in the upper ends of piston chambers 89, gi. However, since ratchets 94, 96 are in their downward positions, neither ratchet wheels 162, 163 is rotated. As a consequence, ball cage 51 does not change its relative position on screw 53 between drive wheel 49 and timing wheel 46, and the rotation of the envases timing wheel d6 will cause cam mechanism at the beginning oi the next gas-lift cycle to open valve 42 after the expiration of a time interval which is the same as that of the preceding cycle.

lf the uid slug reaches the upper end of the production tubing 19 later than it did in the preceding cycle, it is necessary to shorten the cycle. This is accomplished by increasing the rotation of timing wheel 46 as follows. Pressure rise in tubing 19 is transmitted by line 36 to the underside of piston $1, causing the same to rise and the actuation of pivotal member S6, thereby allowing pressure to be released from the upper sides of pistons 92, 93 via lines SS, S7. At the same time, shaft 57 has rotated to a position such that the nozzles of lines 63, 64 are unrestricted by cams 59, 6l, respectively, while the nozzle of line 6d remains restricted by cam 62. rIhus, piston 92 will move upward because the pressure on the lower side thereof is greater than that thereabove together with the downward bias of spring 97. This results in ratchet 94 moving upward and rotation of ratchet wheel 102 in a clockwise direction. Such rotation causes ball cage 5l to move to the right, thereby increasing the rotation of timing wheel d6. Thus, it will take a shorter period of time for cam mechanism 43 to reach its valve actuating position, with'the result that the interval during which oil accumulates in the production tubing will be relatively shorter during the next gaslift cycle.

If the fluid slug reaches the upper end of the production tubing 19 sooner than it did in the preceding cycle, it is necessary to lengthen the cycle. This is accomplished -by decreasing the rotation of timing wheel 45 as follows. Pressure rise in tubing t9 is transmitted by line 36 to the underside of piston 8l, causing the same to rise and the actuation of pivotal member 86, thereby allowing pressure to be released from the upper sides of pistons 92, 93 via lines 88, 87. At the same time, shaft 57 has rotated to a position such that the nozzles of lines 63, 66 are unrestricted by cams 59, 62, respectively, while the nozzle of line 64 remains restricted by cam 6l. Thus, piston 93 will move upward because the pressure on the lower side thereof is greater than that thereabove together with the downward bias of spring 98. This results in ratchet 96 moving upward and rotation of ratchet wheel 103 in a counterclockwise direction. Such rotation lcauses ball cage 5l to move to the left, thereby decreasing the rotation of timing wheel 46. rl`hus, it will take a longer period of time for cam mechanism 43 to reach its valve actuating position, with the result that the interval during which oil accumulating in the production tubing will be relatively longer during the next gas-lift cycle.

The above operations may be understood better by reference to FIGURE 2c, wherein the numeral 6% designates a desired control zone or range. lf the pressure pulse from pressure tap 35 is received while the nozzles of lines 63, 64 and 66 are within control zone 60, no correction is made by the cycle controller. If the pressure pulse is received earlier or later than the desired time so that one of the nozzles 64, 66 is restricted by one of the cams 61, 67;, then the cycle controller will make a correction, in the manner previously described. It is obvious that the extent of the control zone can be changed to shorten or lengthen the same by altering the shape of one or more of the cams.

After the fluid slug is produced, and the pressure of the production tubing returns to its lower bleed pressure, compression spring 83 will cause piston Si to return to rits lower position. Upon the downward movement of appendage 84, the latter in passing the adjacent end of pivotal member 86 is deflected upward, without causing movement of the pivotal member 86. rl`he subsequent restriction of the nozzle of line 87 adjacent the other extremity of pivotal member 86 causes an increase in pressure in the upper ends of pivotal chambers S9, 9i and if either piston 92 or 93 is in its upward position when zthis occurs, said piston will move downward, so that both Cil ratchets 94s, 96 are returned [o their lower position and in condition to be raised, if necessary, during the subsequent cycle. Pivotal member Se may be dampened in its movement, if desired, by any known means such as a dash-pot. This will result in the nozzle of pipe S7 being uncovered for a longer time to insure proper operation of piston 92 or 93.

Although l have described and illustrated a hydraulic operated programmer, it is, of course, within the scope of this invention to employ either an electrical or mechanical-actuated programmer, or combinations thereof; such systems wil-1 be readily apparent to those skilled in the art upon being acquainted with this invention. For example, the cams 59, 61, and 62, pivotal member 86, and shaft 44 of timing well 46 can be designed to actuate suitable electrical switches, and pistons 7 i, 94, and 96 can be o erated by suitable solenoids when the appropriate switches are actuated.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention and it should be understood that this invention is not to -be unduly limited to that set forth herein for illustrative purposes.

I claim:

l. A method of lifting a liquid fr-om a source thereof, which comprises injecting compressed gas int-o a column of said liquid communicating with said source thereby elevating a portion of said column of liquid to a desired elevation, sensing the time of arrival of said p-ortion of said column of liquid at said elevation, comparing said time of arrival with the time of commencement of said step of gas injection to determine the interval therebetween, comparing said interval with a predetermined interval so as to determine the deviation therefrom, passing the thus elevated liquid to a point of use, terminating the injection of gas, thereby permitting said liquid from said source to accumulate to form another column of liquid, controlling the interval of `said accumulating step in accordance with the determined deviation to produce a substantially constant amount of liquid per cycle, and repeating the above cycle of steps.

2. A method of lifting a liquid from a source thereof comprising a tubing depending and communicating with said source, the steps comprising injecting compressed gas into a column of said liquid within the lower end of said tubing thereby elevating a portion of said column of liquid yin the form of a slugy to a desired elevation, the arrival of said slug increasing the pressure within said tubing at said desired elevation, sensing the increase in pressure and converting the same into a signal, comparing said signal on a time scale with another signal indicative of the commencement of the gas injection step to determine the interval therebetween. comparing said interval with a predetermined interval so as to determine the deviation therefrom. passing the thus elevated slug to a point of use. terminatinfy said gas injection step, thereby permitting liquid from said source to accumulate to form another column of liquid in said tubing, the interval of the accumulating step being terminated when said gas is iniected at the beginning of another cycle, controlling the initiation of this latter step of gas injection in accordance with the determined deviation so as to produce a substantially constant amount of liquid per cycle, and repeating the above cycle of steps.

3. A method of lifting oil from an oil well comprising a casing having a production tubing depending therein and communicating at its lower end with an oil producing formation, the steps comprising injecting compressed gas into the upper end of the annulus formed between said casing and tubing, passing said compressed gas from said annulus into a column of oil accumulated in the lower end of said tubing thereby elevating a portion of said column of oil in the form of a slug to a desired elevation at the surface of said well, the arrival of said slug increasing the pressure within said tubing at said desired elevation, sensing the increase in pressure and converting the same into a signal, automatically comparing said signal on a time scale with another signal indicative of the commencement of the gas injection step to determine the interval therebetween, automatically comparing said interval with a predetermined interval so as to determine the deviation therefrom, passing the thus elevated slug to a point of use, terminating the gas injection step, thereby perrnittin.o oil from said source to accumulate to form another column of oil in said tubing, the interval of the accumulation being terminated when said gas injected at the beginning of another cycle, anton ticaliy control ling the initiation of this `iatter step of gas injection in accordance with the determined deviation so as to produce a substantially constant amount of oil cycle, and repeating the above cycie of steps.

4. Apparatus for lifting a liquid from a source thereof, comprising a tubing depending into and communicating at its lower end with said source of liquid, said tubing being adapted to accumulate a column of said liquid within the lower end thereof and permit the elevation of a portion thereof in the form of a slug, injection means operatively connected to said tubing for injecting compressed gas into said column of liquid, timer means connected to said injection means and operatively adapted to control the same, means in uid communication with said tubing to pass the thus elevated slug of liquid to a point of use, sensing means operatively connected to said tubing and adapted to sense the arrival of said slug of liquid at a desired elevation, and automatic cycle controller means connected to said injection, timing, and sensing means and adapted to automatically determine the interval between the gas injection and said arrival of said slug and compare said interval with a predetermined interval to determine deviations therefrom and reset said timer means in accordance with said deviations so as to produce a substantially constant amount of liquid from said source per cycle.

5. Apparatus for lifting a liquid from a source thereof, comprising a well, a production tubing depending within said well and communicating at its lower end with said source, said tubinf being adapted to accumulate a column of said liquid within the lower end thereof and permit 'he elevation of a portion thereof in the form of a slug, injection means operatively connected to said tubing for injecting compressed gas into said `column of liquid, means to pass the thus elevated slug of liquid to a point of use, sensing means adapted to sense: the arrival of said slug of liquid at a desired elevation, means to convert the sensed arrival into a signal, means to compare said signal on a time scale with a signal indicative of the time ot the gas injection to determine the interval therebetween, means to compare said interval with a predetermined interval to determine the deviation therefrom, and means to control said injection means in accordance with said deviation so as to produce a substantially constant amount of liquid from said Well per cycle.

An intermittent gas-lift oil well comprising a casing, production tubing depending within said casing with an annulus formed therebetween, the lower end of said tubing communicating with an oil producing formation, said tubing being adapted to accumulate a coiumn of oil within the lower end thereof and enable a slug of oil to be elevated therein to the surface of said Well, a lift gas supply line connected to the upper end of said annulus, a flow control valve within said lift gas supply line, a line connected to the upper end of said tubing and adapted to pass the thus elevated sing to a point of use, timer means connected to sai-d ilov/ control valve controlling the opening thereof, gas-lift valve means in said tubing adapted to pass compressed gas from said annulus into said column of oil within said tubing to elevate said slug, sensing means operatively connected to said tubing and adapted to sense an increase in pressure in said tubing due to the arrival of said elevated slug at a desired elevation at the surface of said Well, means to convert the sensed arrival into a signal, means to compare said signal on a time scale with a signal indicative of the time ci the gas injection to determine the interval therebetween, means to compare said interval with a predetermined interval to determine the deviation therefrom, and means connected to said timer means to reset said timer means in accordance with said deviation so as to produce a substantially constant amount of liquid from said well per cycle.

litetierences -Cited in the lc of this patent UNITED STATES PATENS 

